San Francisco 49ers' Chris Borland celebrates after a tackle against the New York Giants in the fourth quarter at MetLife Stadium on November 16, 2014 in East Rutherford, New Jersey. (Al Bello/Getty Images)

View FullscreenClose

Marion Bartoli

Marion Bartoli, the 2013 Wimbledon women's singles tennis champion, announced her retirement after losing to Simona Halep of Romania at the Western & Southern Open tennis tournament, Wednesday, Aug. 14, 2013, in Mason, Ohio. Bartoli said constant pain from injuries forced her to quit. (David Kohl/AP)

View FullscreenClose

Ilya Kovalchuk

The star winger stunned the hockey world on July 11, 2013, by calling it quits at age 30. Kovalchuk walked away from $77 million, the amount remaining on his contract, to return to his native Russia. Kovalchuk might not be out of action for long; reports quickly surfaced that he was eyeing a move to the KHL. (Jason DeCrow/AP)

View FullscreenClose

Earvin 'Magic' Johnson

The LA Lakers' superstar point guard was 32 when he announced on Nov. 7, 1991, that he was leaving basketball after testing positive for HIV. Lakers owner Jerry Buss and Johnson's wife, Cookie, look on. Johnson, improbably, made a brief return to the NBA in the 1995-96 season. (Nick Ut/AP)

View FullscreenClose

Michael Jordan

Michael Jordan said goodbye to basketball for the first time on Oct. 6, 1993, at age 30. MJ's Chicago Bulls had three-peated the previous summer, and he was the Finals MVP. His Airness tried his hand at baseball, but after one humbling minor league season, he returned to the Bulls and led the franchise to another set of back-to-back-to-back titles. (Mark Elias/AP)

View FullscreenClose

Barry Sanders

Barry Sanders bowed out in 1999 before he could break Jim Brown's career rushing record, and he did so in the same understated manner in which played. "My desire to exit the game is greater than my desire to remain in it. I have searched my heart through and through and feel comfortable with this decision," Sanders said at the time. (Duane Burleson/AP)

View FullscreenClose

Pat Tillman

The Arizona Cardinals defensive back walked away from the NFL at age 27 to serve his country. Tillman became a U.S. Army Ranger, only to be killed in action in Afghanistan in 2004. His death remains a source of controversy. (Photography Plus via Williamson Stealth Media Solutions/AP)

View FullscreenClose

Lou Gehrig

The Iron Horse bows his head prior to making his "luckiest man on the face of the earth" speech at Yankee Stadium on July 4, 1939. Gehrig died less than two years later at age 37 of amyotrophic lateral sclerosis, a rare disease that today bears his name. (Curtis Management Group/Sporting News Archives)

View FullscreenClose

Kirby Puckett

The Minnesota Twins center fielder retired on July 12, 1996, at age 36 because of a serious eye injury. The 10-time All-Star was suffering from glaucoma in his right eye, and an operation revealed irreversible damage to the eye. The previous September, Puckett was hit in the face by Dennis Martinez. At left is Puckett's wife, Tonya. Kirby Puckett died in 2006 at age 45. (Tom Olmscheid/AP)

View FullscreenClose

Otto Graham

Ten seasons in pro football were enough for Otto Graham, right, shown here with his father, Otto Sr., after Graham quarterbacked the Cleveland Browns to the 1954 NFL championship. The eventual Hall of Famer retired a year later at age 34. (AP Photo)

Advertisement

View FullscreenClose

Rocky Marciano

World heavyweight champion Rocky Marciano rests his head and hand at a news conference in New York on April 27, 1956 after announcing his retirement from boxing. Marciano, undefeated in 49 professional bouts, said his wife Barbara influenced his decision to hang up his gloves. He made an estimated $1.7 million in his boxing career. (AP Photo)

View FullscreenClose

Sandy Koufax

LA Dodgers ace Sandy Koufax tells a news conference in Beverly Hills, Calif., on Nov. 18, 1966, that he is bowing out of baseball at age 30 because of fears he may permanently harm his arthritic left arm. He said the pain in his pitching elbow had grown progressively worse since it began three years earlier. Koufax was at the top of his game when he retired; he registered a career-best 1.73 ERA in 323 innings and struck out 317 batters in his final big league season. (AP Photo)

View FullscreenClose

Joe Namath

On June 6, 1969, less than five months after winning Super Bowl III, a tearful Broadway Joe told the world he'd rather stop playing football than cave to NFL pressure to give up his interest in Bachelors III, a New York restaurant that allegedly had ties to organized crime. A little over a month later, Namath and NFL commissioner Pete Rozelle hammered out a deal in which the QB agreed to sell his stake and return to the field with the New York Jets. Namath never returned to the Super Bowl. (Marty Lederhandler/AP)

View FullscreenClose

Annika Sorenstam

Annika Sorenstam set up a farewell tour for herself when she announced on May, 14, 2008, that she was leaving the course after 93 career victories. “I have other priorities in my life,” she said, including getting married. Sorenstam has become a businesswoman and course designer in her post-golf days. (Wally Santana/AP)

View FullscreenClose

Urban Meyer

Citing health issues and a need to spend more time with his family, Urban Meyer announced on Dec. 8, 2010, that he was stepping down as Florida football coach. Meyer, just 46 at the time, was out of coaching for just one season; he returned to the sideline as Ohio State's coach after the 2011 season and led the on-probation Buckeyes to a 12-0 record last year. (John Raoux/AP)

View FullscreenClose

Ken Dryden

The Cornell-educated goaltender was a six-time Stanley Cup winner and a five-time Vezina Trophy winner, all in just eight seasons with the Montreal Canadiens from 1971 to 1979. With no on-ice worlds left to conquer, Dryden left hockey at age 31. He later became an NHL executive (Maple Leafs) and a member of the Canadian Parliament. (AP Photo)

View FullscreenClose

Bjorn Borg

The Swedish tennis legend was just 26 when he hung up his racket in 1983. At the time, he had won five Wimbledon titles (consecutively from 1976 through 1980) and 11 majors overall. Borg tried to come back a decade later but enjoyed little success. (AP Photo)

View FullscreenClose

Jim Brown

The greatest running back of his era, and perhaps of all time, Jim Brown went out on his terms at age 29 after the 1965 NFL championship game. The Cleveland Browns icon had just won his third consecutive rushing title and eighth overall. Brown soon found his way to Hollywood where he took up acting full time. (AP Photo)

View FullscreenClose

John Moffitt

John Moffitt said playing football was no longer fun for him, so the Denver Broncos offensive lineman decided to retire — and give up his $1 million salary.

"I just really thought about it and decided I'm not happy. I'm not happy at all," Moffitt told The Associated Press in a phone interview from Seattle. "And I think it's really madness to risk your body, risk your well-being and risk your happiness for money. (Gerry Broome/AP)